In recent years, pneumatic and vacuum systems have been developed for removing the contents of railway hopper cars having one or more hopper sections. Other systems use rack and pinion assemblies to open and close a gate valve. These systems have generally been designed to operate in conjunction with a gate valve mounted adjacent to the bottom of each hopper section of the railway car to control the discharge of materials from the associated hopper section.
Railway hopper cars often include one or more hopper sections with each hopper section having a discharge opening through which various types of material and/or lading may be discharged by gravity and/or pneumatic pressure. Typically a gate valve assembly including a gate and a frame assembly are mounted on each discharge opening. The gate and frame assembly cooperate with each other to allow longitudinal movement of the gate between a first, closed position and a second, open position to control the discharge of material from the respective hopper section of the railway car.
Railway hopper cars are often subjected to impact forces which can be quite severe. Therefore, it is important to prevent undesired opening of the gate valve assemblies associated with a hopper car. Various types of locking mechanisms have been previously provided to maintain the associated gate valve assembly in its closed position. Examples of such gate valves and locking mechanisms are shown in U.S. Pat. No. 5,353,713. Also, a wide variety of gate valves have previously been used with railway hopper cars. U.S. Pat. No. 5,285,811 provides one example of such gate valve assemblies. Both of these patents are incorporated by reference for all purposes within this application.
Gate valve assemblies associated with railway hopper cars are often subjected to harsh operating conditions and frequent cycling between open and closed positions. Therefore, it is important to provide a reliable seal or material barrier when the gate valve assembly is in its closed position to prevent any undesired leakage of material from the associated railway hopper car. It is also necessary to prevent leakage into the hopper car.